R-Value Part 2: The Science of Performance

Part Two: The Science of Performance  

In the first part of this article, we learned that ICFs are a superior form of construction (click for part 1) through simplicity of construction, fewer materials, disaster resilience, and insulation performance. So let’s talk a bit more about actual R-value versus performance R-value. All types of building insulation have two levels of performance: material performance and in-use performance. It’s no different than “estimated” miles per gallon when you buy a car; real-world performance is always different. In the case of ICFs, the real world, in-use performance is actually higher than the R-value performance of the raw materials. For most other types of insulation, the opposite is true (less performance R-value when in use).
ICFs are generally 2.5” thick EPS foam panels that are connected together with plastic webs. These webs typically include embedded stud flanges and are spaced evenly inside the panel. Together they create a form for making an insulated concrete sandwich. Why 2.5” you might ask? We’ll cover more in the next article, but based on independent testing, 2.5” panels (5” total) delivers so much insulation value that adding more doesn’t make much of a difference. Also, at 2.5” with 6” on center web spacing, BuildBlock ICFs are strong enough to not deflect, break, bulge or crack when filled with concrete and rebar.

So all these claims…”Where’s the beef?”

The short version goes like this. The ICF industry went to an independent ISO & SCC certified lab to do open ASTM performancestandards-based testing (yes, the short version is fairly technical). The lab compared a code-compliant 2×6 wood framed cavity wall (actually built better than most homes) to a standard 6-inch core ICF wall.

Nothing special was done to the ICF wall. It was stacked, reinforced, poured, and cured for 30 days.

The lab then subjected one side of each wall to extremely cold temperatures (-35°). At that temperature °F & °C are basically the same number. While cooling the outside they measured the amount of energy needed to maintain the interior temperature at a constant room temperature (70°F/22°C). In technical terms, this is called steady state. What matters is they did the same test for each wall.

What happened?

At steady state, the wood framed cavity wall took 39.9kWh (132,828 BTU) to maintain a constant temperature. The standard ICF wall only took 15.6kWh (53,209 BTU) to do the same work. That’s 2.5X the amount of heat needed, or more simply, 2.5X more money. If that were a monthly electrical bill, the wood frame wall would cost you $132 and the ICF wall $53. That adds up quickly.

If you’d like the long version, visit the Performance section of our website and download the full study.

Okay, so ICF good, wood frame cavity wall bad. I get it. So now what? 

In the next section of this article, we’ll discuss why the foam panels are important and how foam thickness determines R-value. Do thicker panels make for drastically more efficient walls? The answer might surprise you. Click here for part 3.

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